# Step 4: Create an AWS IoT rule to send an email
<a name="iot-moisture-create-rule"></a>

An AWS IoT rule defines a query and one or more actions to take when a message is received from a device. The AWS IoT rules engine listens for messages sent by devices and uses the data in the messages to determine if some action should be taken. For more information, see [Rules for AWS IoT](iot-rules.md). 

In this tutorial, your Raspberry Pi publishes messages on `aws/things/RaspberryPi/shadow/update`. This is an internal MQTT topic used by devices and the Thing Shadow service. The Raspberry Pi publishes messages that have the following form:

```
{
    "reported": {
        "moisture" : moisture-reading,
        "temp" : temperature-reading
    }
}
```

You create a query that extracts the moisture and temperature data from the incoming message. You also create an Amazon SNS action that takes the data and sends it to Amazon SNS topic subscribers if the moisture reading is below a threshold value.

**Create an Amazon SNS rule**

1. In the [AWS IoT console](https://console.aws.amazon.com/iot/home), choose **Message routing** and then choose **Rules**. If a **You don't have any rules yet** dialog box appears, choose **Create a rule**. Otherwise, choose **Create rule**.

1. In the **Rule properties** page, enter a **Rule name** such as **MoistureSensorRule**, and provide a short **Rule description** such as **Sends an alert when soil moisture level readings are too low**.

1. Choose **Next** and configure your SQL statement. Choose **SQL version** as **2016-03-23**, and enter the following AWS IoT SQL query statement:

   ```
   SELECT * FROM '$aws/things/RaspberryPi/shadow/update/accepted' WHERE state.reported.moisture < 400
   ```

   This statement triggers the rule action when the `moisture` reading is less than `400`.
**Note**  
You might have to use a different value. After you have the code running on your Raspberry Pi, you can see the values that you get from your sensor by touching the sensor, placing it in water, or placing it in a planter. 

1. Choose **Next** and attach rule actions. For **Action 1**, choose **Simple Notification Service**. The description for this rule action is **Send a message as an SNS push notification**.

1. For **SNS topic**, choose the topic that you created in [Step 3: Create an Amazon SNS topic and subscription](iot-moisture-create-sns-topic.md), **MoistureSensorTopic**, and leave the **Message format** as **RAW**. For **IAM role**, choose **Create a new role**. Enter a name for the role, for example, **LowMoistureTopicRole**, and then choose **Create role**.

1. Choose **Next** to review and then choose **Create** to create the rule.